Die pads for ram type presses



Sept. 8, 1964 F. M. wn |v |AMsoN 3,147,722

DIE PADS FoR RAM TYPE PRESSES Filed May 19. 1961 2 sheets-sneer 1 i E EEL A 7i fw M i Sept. 8 1964 F. M. WILLIAMSON IDIIEI PADS FOR RAM TYPE PRESSES Filed May 19, 1961 2 Sheets-Sheet 2 INVENToR. )7a/.57 /Yh/zL/Zzdmfaff l BY 2F United States Patent O 3,147,722 DIE PADS FUR RAM TYPE PRESSES Floyd M. Williamson, Dfi-Dro Engineering Company, 2405 E. Grand Blvd., Detroit 11, Mich. Filed May 19, 1961, Ser. No. 111,287 14 claims. (ci. 113-42) This invention relates to a ram type press having a set of die members and hydraulic control means for the die members adapted to perform multiple operations on a workpiece during each cycle of the press. More particularly, the invention relates to a press of this type provided with relatively movable upper and lower die members and hydraulic pressure pads associated with the movable die members to provide a predetermined resistance to movement thereof during closing of the press and to perform an additional operation on the workpiece as the ram begins its return stroke. A system of this type is particularly useful in performing a curling operation on the edge of the workpiece on the return stroke of the ram, the workpiece being formed to the desired shape as the press closes.

A principal object of the invention is to provide a ram type press having a set of dies and hydraulic control means for the dies to effect a forming operation on a workpiece upon closing of the press and to effect a further operation on the workpiece as the press begins to open.

Another object of the invention is to provide a press of the type described wherein the edge of the workpiece is curled or rolled during the return stroke of the ram. p Another object of the invention is to provide a press of the type described adapted to perform multiple operations on a workpiece during each stroke of the press While preventing wrinkling or distortions in the part.

Cther and further objects of the invention will be apparent from the following description and claims and may be understood by reference to the accompanying drawings, of which there are two sheets, which by way of illustration show preferred embodiments of the invention and what I now consider to be the best mode of applying the principles thereof. Other embodiments of the invention may be used without departing from the scope of the present invention as set forth in the appended claims.

In the drawings:

FIG. l is a sectional somewhat schematic view of a set of dies and the hydraulic control system therefor and showing the workpiece after it has been fully formed by the dies;

FIG. 2 is a fragmentary sectional view showing a modication of a part of the apparatus shown in FIG. 1;

FIG. 3 is a fragmentary view similar to FIG. 1 showing the relative position of the dies as the ram begins its working stroke;

FIG. 4 is a view similar to FIG. 3 showing the parts as the ram nears the bottom of its stroke; and

FIG. 5 is a view similar to FIGS. 3 and 4 but showing the position of the die members when the ram is at the bottom of its stroke.

In FIG. l there is shown an upper die shoe which is secured to and adapted to be reciprocated by the ram (not shown) of any conventional ram type press. The die shoe 10 carries a forming die 12 and a cut-olf die 14, both of which are xedly secured to the upper die shoe 10. A forming die member 16 is also carried by the upper die shoe 10 but is reciprocable relative to the die members 12 and 14.

The stationary lower die shoe 18 is provided with a stationary cut-off die 20 and a forming die 22 which is vertically reciprocable relative to the cut-olf die 20 and die shoe 18. p

The upper movable die member 16 is provided with a 3.147322 Patented Sept. 8, 1964 ICC hydraulic cushion consisting of cylinders 24 having pistons 26 reciprocable therein having their lower ends reacting against the die member 16. The cylinders 24 are adapted to be supplied with hydraulic fluid under pressure so as to force the pistons 26 downwardly to hold the die member 16 in its extended position relative to the die shoe 10. The lower forming die 22 is also provided with a hydraulic cushion which comprises cylinders 28 having pistons 30 therein which are urged upwardly by hydraulic iiuid under pressure supplied to the cylinders 28 to hold the die member 22 in its extended position relative to the lower die shoe 18. The hydraulic cushions are adapted through the control system to be described to provide a predetermined amount of resistance to movement of the movable die members 16 and 22 to their retracted positions and'to effect a further forming of the workpiece 32 as the ram begins its return stroke.

The hydraulic control system for the hydraulic cushion includes a tank 34 containing hydraulic fluid such as oil under relatively low air pressure which is supplied from a line 36 leading from a source of air under pressure. The oil is supplied to the cylinders 24 through a line 38 past check valves 40 and 42 which prevent return llow from the cylinders 24 back to the tank 34. A preload cylinder 44 is connected into the line 38 between the check valves 40 and 42 and contains a piston 46 adapted to engage a stop block 48 upon closing of the press. A line 50, which is also connected to the conduit 36 leading to the source of air under pressure, supplies the air under pressure to a tank 52 past a check valve 54. A line 56 communicates the tank 52 with a booster cylinder 58 which consists of an air cylinder 60 containing an air actuated piston 62 and a smaller diameter cylinder 64 containing a booster piston 66 which is connected to the air piston 62 by a stem 68. A line 70 leads from the tank 34 to a check valve 72 past which the hydraulic pressure fluid is adapted to be supplied to the cylinder 64 through passages 74 and 76. The passage 74 is connected to the line 38 which leads to the hydraulic cushion cylinders 24. When the air piston 62 is actuated by the air under pressure from tank 52, it will shift the booster piston 66 to the left to greatly increase the pressure in the cylinders 24 above the pressure at which the oil is maintained in the tank 34. When the pistons 26 are forced to their retracted position as the press closes, the hydraulic iluid in the cylinders 24 will be forced out through the line 38 and passages 74 and 76 in the booster unit 58 to force the pistons 66 and 62 to the right and rell the cylinder 64. A pressure relief valve 78 normally closes a return line 80 which is connected into the line 70 and is adapted -to open when the pressure in the cylinders 24 reaches a predetermined pressure for which the valve 78 is set to permit the oil in the cylinders 24 to flow back to the supply tank 34. The pressure relief valve 78 provides a predetermined resistance to movement 0f the die member 16 to its retracted position.

A supply 9i) containing hydraulic fluid is supplied with air under pressure through a line 92 to maintain the hydraulic fluid in the tank at a predetermined relatively low pressure. The oil is supplied from the tank through a line 94 to a check valve 96 forming a part of a booster unit 98 and past the check valve through passages 100 and 102 in the check valve body to line 104 from which the oil is supplied to the cylinders 28. A stud 106 is secured to the lower movable die member 22 and extends slidably through an aperture 19S in the lower die shoe 18 which is provided with a counterbore 110. A Washer 112 engages the end of the counterbore 110 and a spring 114 is confined between the washer 112 and a washer 116 which is retained on the lower end of the stud 106 by a nut 118. The spring 114 biases the die member 22 downwardly in opposition to the upward force exerted thereon by the pistons 38 under the pressure of the oil from the tank 98. When the press is open the die member 22 will be in the position shown in FlG. 3 from which it will be seen that the upper surface of the die member 22 is at the same level as the upper surface of the die member 2@ so that the workpiece 32 will lie fiat across the lower die members in position to be gripped by the upper die member 16 as the ram descends.

The booster unit 98 includes an air piston 120 working within an air cylinder 122 and a booster piston 124 reciprocable within a cylinder 126 which communicates with the passage 1811 in the check valve 96 so as to be lled with oil under pressure from the tank 98. The pistons 128 and 124 are connected by a stem 128 for movement together. The cylinder 122 is adapted to be supplied with air under pressure below the piston 128 from a tank 138 containing air under pressure. A valve 132 is interposed in the line 134 which connects the tank 1311 to the cylinder 122. The valve 132 includes an actuating arm 136 adapted to be engaged by a cam 138 on a part 148 which is driven with the crank of the press. The arm 136 of the vaive 132 is adapted to connect the tank 138 to the cy inder 132 or to connect the line 134 to an exhaust line 142 when the arm 136 is actuated by the cam 138.

A return line 144 is connected to the supply line 1114 for the cylinders 28 and to the line 94 which is connected to the supply tank 98. A pressure relief valve 146 is interposed in the line 144 between the cylinders 28 and the tank 98 and is normally closed to provide a predetermined resistance to movement of the die member 22 to its retracted position. When the pressure in the cylinders 28 reaches a predetermined pressure, the relief valve 146 will open to allow the oil trapped in the cylinders 28 to return to the supply tank 90.

The invention is illustrated herein in connection with a workpiece 32 which is to be trimmed to size and formed into any suitable shape such as that shown in FIG. l and also provided with a curl at the edge thereof. At the beginning of a cycle of operation the workpiece is supported on the upper surfaces of the lower die members 28 and 22 with the die member 22 maintained in the position shown in FIG. 3 by the combination of the pressure existing inthe cylinders 28 and the downward force exerted by the spring 114. The upper die member 16 is held in its extended or lower position by the pistons 26 due to the pressure existing in the cylinders 24. Since the booster unit 58 is always actuated, the booster piston 66 will, due to the larger size of the piston 62, force oil under relatively high pressure through the passages 76 and 74 to the line 38 and to cylinders 24. The piston 46 in the pre-load cylinder 44 is also in its extended position at this time. As the ram descends, the die meme ber 16 first engages the workpiece to clamp it between the die member 16 and the opposing lower die member 29. The pressure uid trapped in the cylinders 24 as the ram descends further provides a predetermined resistance to movement of the die member 16 to its retracted position, thereby providing a predetermined clamping force on the workpiece 32. The oil which is forced out of cylinders 24 as the pistons 26 are retracted flows through line 38 and passages 74 and 76 to move pistons 66 and 62 to the right. When the pressure at which the relief valve is set to open is exceeded, the valve will open to return the trapped fluid to the tank 34.

The parts are shown in FIG. 3 with the workpiece 32 partially formed just prior to completion of the downward stroke of the ram. The die member 16 is partially retracted while still maintaining the desired clamping force on the workpiece. The pistons 38 provide a predetermined resistance to retraction of the lower die member 22 and, as the ram completes its downward stroke, the die member 22 is retracted to the position shown in FIG. 5 and the cut-off die 14 trims the workpiece to size. The pre-load piston 46 engages the stop block 48 as the press closes to force oil at high pressure past check valve 42 to the line 38 to return to the system the amount of oil that escapes past relief valve 78.

The die member 16 is provided with a channel or groove 152 into which the edge of the workpiece is forced on the upward stroke of the ram to provide the curl 158 at the edge of the work. As soon as the ram begins its upward stroke, the cam 138, which is driven with the press, is set to actuate the valve 132 to supply air under pressure to the lower side of the piston 128 thereby to force oil under relatively high pressure from the cylinder 126 through passages 186 and 182 to the line 184 and cylinders 28. The lower die member 22 is forced to its extended position as theupper die is raised, keeping the Work firmly engaged between thev die members 12 and 22 and forcing the edge of the work to curl within the groove 152 as the die 22 reaches its fully extended position shown in FIG. 1. It will be noted that those portions of the workpiece immediately adjacent the curl 154.rx are tangent thereto. The upper die member 16 is, of course, moved to its retracted position as the ram reaches the lower end of its stroke and, as the ram begins to raise, the die member 16 is again moved to its extended position relative to the die shoe 18 so as to remain in engagement with the lower stationary die member 28.

After the curling operation is completed, the die member 22 is in its fully extended position in which it projects slightly above the upper surface of the die member 21). The valve 132 is then cycled to connect the air cylinder 122 with the exhaust line 142, thereby reducing the pressure in the cylinders 28 so that the spring 114 is effective to pull the die member 22 down to the starting position shown in FIG. 3.

FIG. 2 illustrates a modified form of the invention in which the valve unit 160 replaces the check valve 96 at the upper end of the booster unit 98. The valve unit 160 consists of a block 162 having a passage 164 therein communicating with the booster cylinder 126 and a passage 166 which is normally closed by a check valve 168. The valve body 170 is provided with an inlet passage 172 to which the line 94 is connected and a passage 174 which communicates with the passage 166 through the check valve 168. A sleeve 176 is disposed within a cavity in the valve body 170 and is provided with radial ports 178 which communicate with passage 172 and a second set of radial ports 180 which communicate with a passage 182 which intersects the outlet passage 184 to which the line 104 is connected. A valve member 186 is urged downwardly by aspring 188 to a position in which it closes off the ports 180 and the upper end of the passage 164. When the booster unit 9S of this modification is energized, oil will be forced out of the cylinder 126 through passage 164 to force the valve member 186 upwardly against spring 188 to open ports 180 and close ports 178. High pressure oil is thereby delivered through passages 182 and 184 to line 104 to move the die member 22 upwardly with the die member 12 to perform the curling operation on the work as the press opens. The booster unit may be actuated slightly before the ram reaches the bottom of its stroke in this modification of the invention. As soon as the valve 132 is shifted to exhaust the air cylinder .122 the spring 188 will shift the valve member 186 to the position shown closing olf ports 188 and opening ports 178. This will immediately relieve the excess pressure in the cylinders 28 by permitting a return flow from the line 1114 back through passage 184, the interior of the sleeve 176 and radial ports 178 and passage 172 to the line 94 and the tank 90. Thus in this modification it is not necessary for the pistons 124 and 128 to move to their retracted position before the die member 22 can be pulled down to its starting position by the spring 114 and this arrangement would be advan tageous at higher speed operations.

This application is a continuation-in-part of my prior Y copending application Serial No. 768,889, filed October 22, 1958, for Hydraulic Press Ram Cushion, now Patent No. 3,085,530; of my prior copending application Serial No. 863,315, tiled December 3l, 1959, for Hydraulic System for Dies; and of my prior copending application Serial No. 88,092, led February 9, 1961, for Ram Type Press.

While I have illustrated and described preferred embodiments of my invention, it is understood that these are capable of modification, and I therefore do not wish to be limited to the precise details set forth but desire to avail myself of such changes and alterations as fall within the purview of the following claims.

I claim: 1. In a ram press adaptedto perform multiple operations on a workpiece during each cycle of operation,

a stationary lower die shoe and an upper die shoe adapted to be reciprocated by the ram, a die set comprising a die member movably mounted on each of said die shoes and a cooperating die member for each movable die member xedly mounted on the other die shoe, a hydraulic cushion for each of said movable die members comprising a cylinder having a piston therein reacting against said movable die member, a source of hydraulic iluid under pressure, fluid connections between said source and said cylinders through which fluid is supplied to said cylinders to actuate said pistons and thereby move said movable die members to their extended positions relative to said die shoes, a check valve in said connections preventing return flow therethrough, a by-pass around each check valve and a normally closed pressure relief valve in said by-pass to provide a predetermined resistance to movement of said movable die members to their retracted positions upon closing of the press, a booster cylinder comrnimicating with the hydraulic cushion cylinder associated with the lower movable die member, and means for Astationary lower die shoe and an upper die shoe adapted l to be reciprocated by the ram, a die set comprising a die member movably mounted on each of said die shoes and a cooperating die member for each movable die member iixedly mounted on the other die shoe, a hydraulic cushion for each of said movable die members comprising a cylinder having a piston therein reacting against said movable die member, a source of hydraulic fluid under pressure, iluid connections between said source and said cylinders through which fluid is supplied to said cylinders to actuate said pistons and thereby move said movable die members to their extended positions relative to said die shoes, a

`check valve in said connections preventing return ow therethrough, a return line from said cylinders to said v pressure fluid source and a normally closed pressure relief v valve in each return line to provide a predetermined resistance to movement of said movable die members to 4their retracted positions upon closing of the press, a booster cylinder communicating with the hydraulic cushion cylinder associated with the lower movable die member, and means for actuating said booster cylinder as the ram reaches the bottom of its stroke to increase the pressure in said last-mentioned hydraulic cushion cylinder above the pressure supplied thereto from said source of iluid under pressure to force said lower movable die member upwardly with its cooperating upper die member while said upper movable die member is moved to its extended position so as to remain stationary as the ram begins its return stroke, thereby to perform an additional operation on the workpiece between said movable die members during said return stroke of the ram.

3. A press according to claim 2 wherein said booster cylinder is interposed in said uid connection to said one hydraulic cushion cylinder between the check valve in said connection and said one cylinder.

4. A press according to claim 2 wheren said actuating means is operated in timed relation to operation of the press.

5. A press according to claim 2, including a valve in the connection between said booster cylinder and said one hydraulic cushion cylinder, said valve in one position thereof closing said connection while providing a direct connection between said one cylinder and said source of pressure iluid, said valve being actuated by said booster cylinder to close said direct connection and open said iluid connection through said check valve.

6. A press according to claim 2, including a pair of check valves in said iiuid connection to the hydraulic cushion cylinder for said upper movable die member and a pre-load cylinder connected between said check valves and having a piston therein actuated upon closing of the press to supply fluid 4to said hydraulic cushion cylinder to compensate for the fluid which escapes past the relief valve in said return line from such cylinder.

7. In a ram press adapted to perform multiple operations during each cycle of press operation on a workpiece positioned between the opposed dies of the press and having a stationary die shoe and a movable die shoe reciprocated with the press ram as it closes and opens, a rst pair of opposed forming dies comprising a die member movably mounted on one of said die shoes for movement between extended and retracted positions relative thereto -in response to closing and opening of the press ram and a cooperating die member ixedly mounted on the other die shoe, and a second pair of opposed forming dies comprising a die member ixedly mounted on said one die shoe and a die member movably mounted on said other die shoe for movement between extended and retracted positions relative thereto` in response to closing and opening movement of the press r-am; a hydraulic cushion reacting on each of said movable die members for urging it toward its extended position and for resisting retraction thereof upon closing of the press ram, said hydraulic cushion for one of said movable die members comprising a cylinder and piston arranged to react against said one of said movable die members, a source of hydraulic Huid under pressure, hydraulic fluid and pressure transmitting connections between said source and said cylinder through which Huid under pressure is supplied to said cylinder and piston to thereby force the associated movable die member toward its extended position relative to its die shoe, valve means in said connections providing a predetermined resistance higher than source pressure to displacement of hydraulic lluid from said cylinder so as to provide a predetermined resistance to movement of the associated movable die member to its retracted position upon closing of the press ram, a hydraulic pressure booster communicating with the hydraulic cushion cylinder associated with said one of said movable die members, means for actuating said booster at the bottom of the closing stroke of the ram so as to increase the pressure in said last-mentioned hydraulic cushion cylinder above the pressure supplied thereto from its source so as to move said one of said movable die members with its cooperative die member and the ram as the ram begins its opening stroke, the hydraulic cushion associated with the other movable die member being operable to maintain the hydraulic pressure thereon so as to move the latter toward its extended position during opening movement of the ram for cooperation with its opposed forming die and the other forming dies, thereby to perform an additional operation on the workpiece during said opening stroke of the ram.

8. A ram press according ot claim 7 wherein said hydraulic cushion for said other movable die member continuously maintains a hydraulic pressure thereon of the same order of magnitude as the pressure developed by said hydraulic pressure booster.

9. A ram press according to claim 7 wherein said hydraulic cushion for said other movable die member comprises a cylinder and piston arranged to react against said other movable die member, ya tank of hydraulic uid under relatively low pressure, hydraulic fluid and pressure transmitting connections between said tank and lastmentioned cylinder through which hydraulic iiuid under tank pressure is supplied to said last-mentioned cylinder for forcing said other movable die member toward its extended position relative to its die shoe, valve means in said last-mentioned connections providing a predetermined resistance higher than tank pressure to displacement of hydraulic fluid from said last-mentioned cylinder` so as to provide a predetermined resistance to movement of said other movable die member to its retracted position upon closing of the press ram, a hydraulic pressure booster communicating with the last-mentioned cylinder to maintain the hydraulic pressure therein above tank pressure and thereby move the latter toward its extended position during opening movement of the ram for cooperation with its opposed forming die and the other forming dies thereby to perform an additional operation on the Workpiece during the opening stroke of the ram, and a preloading `cylinder supplied with hydraulic fluid under pressure from said tank and operable in response to closing movement of the press r-am for supplying hydraulic uid under pressure greater than tank pressure to the hydraulic cushion cylinder for said other movable die member prior to the closing movement of the press ram.

10. A press according to claim 7 wherein the parting line of said pair of forming dies which move with the ram as it begins its opening stroke moves across the parting line of the other pair of forming dies so that a portion of the workpiece engaged by the latter is thereby displaced relative to other portions of the workpiece.

11. A press according to claim 7 wherein one of said pair of forming dies forms a combined curling die and draw pad.

12. In a ram press adapted to perform multiple operapiece positioned between the opposed dies of the press and j' having a stationary die shoe and a movable die shoe reciprocated with the press ram as it closes and opens, a first pair ofopposed forming dies comprising a die member movably mounted on one of said die shoes for move- Y ment between extended and retracted positions relativev thereto in response to closing and opening of the press -ram and a cooperating die member ixedly mounted on the other die shoe, and a second pair of opposed forming dies comprising adie member ixedly mounted on said` one die shoe and a die member movably mounted on saidI other die shoe for movement between extended and retracted positions relative thereto in response to closing and opening movement of the press ram; a hydraulic cushion reacting on each of said movable die members for urging it toward its extended position and for resisting said cylinder so as to provide a predetermined resistance to movement of the associated movable die member to its retracted position upon closing of the press ram, a hydraulic pressure booster communicating with the hyydraulic cushion cylinder associated vwith one of said movable die members, means for actuating said booster at the bottom of the closing stroke of the ram so as to increase the pressure in said last-mentioned hydraulic -cushion cylinder above the pressure supplied thereto from its source so as to move said one of said movable die :members with its cooperating die member and the ram as the ram begins its opening stroke, and a hydraulic pressure booster communicating with the hydraulic cushion associated with the other movable die member to maintain the hydraulic pressure thereon above the source pressure and thereby move the latter toward its extended position during opening movement of the ram for cooperation with its opposed forming die and the other formingdies, thereby to perform an additional operation -on the workpiece'during said opening stroke of the ram.

13. A press ram according to claim 12 including spring v means for normally positioning said one of said movable ldie members at the llevel of the clamping surface of the xed die member of the other pair of forming dies.

14. In a ram press adapted to'perform multiple operations during each cycle of press operation on a workpiece positioned between the opposed dies ofthe press and hav- :ing a stationary die shoe and a movable die shoe recipro- 4cated with the press ram as it closes and opens, a rst pair of opposed forming dies comprising a die member movably mounted on one of said die shoes for movement between extended and retracted positions relative thereto in response to closing and opening of the press ram and a cooperating die member xedly mounted on the other die shoe, and a second pair of opposed forming dies comprising a die member xedly mounted on said one die shoe and a die member movably mounted on said other die shoe for movement between extended and retracted positions relative thereto in response to closing and opening movement of the press ram; a hydraulic cushion reacting on each of said movable die members for urging it toward its extended position and for resisting retraction thereof upon closing of the press ram, said hydraulic tions during each cycle of press operation on a work- ,45 I

cushion for one of said movable die members comprising a cylinder and piston arranged to react against said one of said movable die members, a source of hydraulic fluid under pressure communicating with said cylinder and piston to thereby force said one of said movable die mem- 'bers toward its extended position relative to its die shoe,

valve means providing a predetermined resistance higher than source pressure to displacement of hydraulic fluid from said cylinder so as to provide a predetermined resistance to movement of said one of said movable die memvybers' to its retracted position upon closing of the press ram, means operable atthe bottom of the closing stroke of the ram so as to increase the pressure in said hydraulic cushion cylinder above the pressure supplied thereto from its sourceso as to move said one of said movable die members with its cooperating die member and the ram as the ram begins its opening stroke, the hydraulic cushion associated with the other movable die member being operable to maintain the hydraulic pressure thereon so as to move the latter toward its extended position during opening movement of the ram for cooperation with its opposed forming die and other forming dies, thereby to perform an additional operation on the workpiece during said opening stroke of the ram.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN A RAM PRESS ADAPTED TO PERFORM MULTIPLE OPERATIONS ON A WORKPIECE DURING EACH CYCLE OF OPERATION, A STATIONARY LOWER DIE SHOE AND AN UPPER DIE SHOE ADAPTED TO BE RECIPROCATED BY THE RAM, A DIE SET COMPRISING A DIE MEMBER MOVABLY MOUNTED ON EACH OF SAID DIE SHOES AND A COOPERATING DIE MEMBER FOR EACH MOVABLE DIE MEMBER FIXEDLY MOUNTED ON THE OTHER DIE SHOE, A HYDRAULIC CUSHION FOR EACH OF SAID MOVABLE DIE MEMBERS COMPRISING A CYLINDER HAVING A PISTON THEREIN REACTING AGAINST SAID MOVABLE DIE MEMBER, A SOURCE OF HYDRAULIC FLUID UNDER PRESSURE, FLUID CONNECTIONS BETWEEN SAID SOURCE AND SAID CYLINDERS THROUGH WHICH FLUID IS SUPPLIED TO SAID CYLINDERS TO ACTUATE SAID PISTONS AND THEREBY MOVE SAID MOVABLE DIE MEMBERS TO THEIR EXTENDED POSITIONS RELATIVE TO SAID DIE SHOES, A CHECK VALVE IN SAID CONNECTIONS PREVENTING RETURN FLOW THERETHROUGH, A BY-PASS AROUND EACH CHECK VALVE AND A NORMALLY CLOSED PRESSURE RELIEF VALVE IN SAID BY-PASS TO PROVIDE A PREDETERMINED RESISTANCE TO MOVEMENT OF SAID MOVABLE DIE MEMBERS TO THEIR RETRACTED POSITIONS UPON CLOSING OF THE PRESS, A BOOSTER CYLINDER COMMUNICATING WITH THE HYDRAULIC CUSHION CYLINDER ASSOCIATED WITH THE LOWER MOVABLE DIE MEMBER, AND MEANS FOR ACTUATING SAID BOOSTER CYLINDER WHEN THE RAM REACHES THE BOTTOM OF ITS STROKE TO INCREASE THE PRESSURE IN SAID LASTMENTIONED HYDRAULIC CUSHION CYLINDER ABOVE THE PRESSURE SUPPLIED THERETO FROM SAID SOURCE OF FLUID UNDER PRESSURE TO FORCE SAID LOWER MOVABLE DIE MEMBER UPWARDLY WITH ITS COOPERATING UPPER DIE MEMBER AS THE RAM BEGINS ITS RETURN STROKE, THEREBY TO PERFORM AN ADDITIONAL OPERATION ON THE WORKPIECE BETWEEN SAID MOVABLE DIE MEMBERS DURING SAID RETURN STROKE OF THE RAM. 